The present invention generally relates to the measurement of tire uniformity with a tire uniformity machine, and more specifically to the removal of the erroneous contributions of the tire uniformity machine to the tire uniformity measurement signals.
In the art of manufacturing pneumatic tires, rubber flow in the tire mold or minor differences in the dimensions of the belts, beads, liners, treads, plies of rubberized cords, etc., sometimes cause non-uniformities in the final tire. Non-uniformities of a sufficient magnitude will cause force variations on a surface, such as a road, against which the tires roll producing vibration and noise. When such variations exceed an acceptable maximum level, the ride and handling of a vehicle utilizing such tires will be adversely affected.
Tire uniformity machines are used to monitor the quality of the tire production process and may guide or incorporate corrective measures such as grinding to improve the balance and uniformity of a tire. In general, a tire uniformity machine subjects a tire to normal conditions of mounting, pressurization, rotation and load while collecting measurement data on variations of deflection, force, and velocity. A tire uniformity machine (TUM) typically includes an assembly for rotating a tire against the surface of a rotating loading wheel. In this testing arrangement, the loading wheel is acted upon in a manner dependent on the forces exerted by the rotating tire. Resulting deflections, force variations and velocities are measured by appropriately placed measuring devices. When a tire being tested yields unacceptable results, shoulder and/or center rib grinders are used to remove a small amount of the tire tread at precisely the location of the non-uniformities detected by the measuring devices. In a sophisticated tire uniformity machine the measurements are stored and interpreted in digital form by a computer, and rubber is removed from the tire tread using grinders controlled by the computer. Examples of machines utilizing these methods are disclosed in U.S. Pat. Nos. 3,739,533; 3,946,527; 4,914,869 and 5,263,284.
Unavoidably, fire uniformity machines are not themselves perfectly uniform, and so tire uniformity measurement signals may include an erroneous contribution from the tire uniformity machine itself. In effect, minor variations in the design, construction and operation of a tire uniformity machine contribute to variations of deflection, force or velocity that contaminate the tire uniformity measurements with a xe2x80x9cmachine contribution.xe2x80x9d In general, tire uniformity machines are designed, manufactured and operated to minimize the machine contribution to the tire uniformity measurement data. However, there are technical and cost limitations to the precision and care with which a tire uniformity machine can be built and operated such that some machine contribution is inevitable. The prior art provides a variety of examples addressing methods to avoid and correct tire uniformity measurement errors.
As noted by U.S. Pat. No. 4,404,848 (""848), it is often the case that measured values contain errors due to rotational deflections of the rims that grip the inspected tire and/or the load wheel of the tire uniformity machine. In addition, small deflections occur due to the deterioration of parts, by rust or by bruises which are developed during use of the inspecting machines. A method to correct these types of errors is disclosed by the ""848 patent wherein the radial runout of the load wheel is measured without a tire in place to obtain an erroneous deflection signal. The erroneous deflection signal is then multiplied by the spring constant of the measured tire and subtracted from the measured value of the radial force obtained from the tested tire.
U.S. Pat. No. 4,404,849 describes a method for correcting errors of measurement due to variations in tire pressure in a tire uniformity inspecting operation.
U.S. Pat. No. 5,614,676 (""676) describes a method of vibration analysis for tire uniformity machines by using signals from load cells when the machine idles. The signals are sent to a computer that outputs an alarm signal when the amplitude of vibration at selected frequencies exceeds acceptable levels.
Since complete elimination of defects and imperfections of the tire uniformity machine is difficult, it is more practical to measure and then remove the machine contribution from tire uniformity machine measurement signals, thereby improving the quality of the tire uniformity machine measurements which, in turn, improves the efficiency of corrective actions based on those measurements. So there is a need for improved methods to monitor and compensate for these inevitable machine contributions.
The present invention relates to a method for correcting errors of measurement made on tire uniformity machines by removing machine contributions from tire uniformity measurements.
The invention comprises a method to identify and remove a machine contribution from tire uniformity measurements made on a tire uniformity machine which subjects a tire to normal conditions of mounting, inflation, load and rotational speed while measuring and collecting tire uniformity measurement data with respect to a rim reference mark, the method characterized by the steps of:
step 1: mounting a tire on the tire uniformity machine at a random angular position with respect to the rim reference mark;
step 2: collecting tire uniformity data to record a first measurement of uniformity data set;
step 3: re-mounting the same tire on the tire uniformity machine at a random angular position with respect to the rim reference mark;
step 4: collecting tire uniformity data to record a repeated measurement of uniformity data set;
step 5: determining if additional measurements of uniformity are required for the tire, then looping back to repeat steps 3 through 5 if additional measurements of uniformity are determined to be required, but proceeding to step 6 when it is determined that additional measurements of uniformity are not required;
step 6: calculating cross-correlation functions and using them to determine angular shifts between the first measurement data set and each of the repeated measurement data sets;
step 7: using the angular shifts to synchronize each repeated measurement data set with the first measurement data set to yield synchronized measurement of uniformity data sets; and
step 8: averaging together the first measurement of uniformity data and all of the synchronized measurement of uniformity data sets to yield an average tire uniformity data set that has minimized both random measurement noise and machine contribution errors in the measurement of uniformity data for the tire.
According to invention, the step 5 is further characterized by determining a required quantity of additional measurements of uniformity for the tire by quantifying and using knowledge of a random variability of tire uniformity measurements through statistical analysis of multiple repeated measurements of tire uniformity on the tire uniformity machine. Alternatively, the step 5 is further characterized by determining a required quantity of additional measurements of uniformity for the tire by specifying the required quantity as a fixed quantity in the range of 20 to 50.
Also according to the invention, the method comprising steps 1 through 8 is further characterized by storing and interpreting the measurement of uniformity data, performing calculations, and processing corrective actions in digitized forms in an arithmetic operation circuit.
According to invention, the method comprising steps 1 through 8 may be characterized in that the steps 1 through 8 are performed using a test tire for the tire, the test tire being selected to be representative of a group of tires to be measured on the tire uniformity machine. The method then comprises the additional steps of:
step 9: using the angular shifts to synchronize the average test tire uniformity data set with each of the repeated measurement of uniformity data sets, and then subtracting to determine the machine contribution in each test tire measurement of uniformity data set to yield machine contribution data sets;
step 10: averaging together all of the machine contribution data sets to yield an average machine contribution data set for the test tire;
step 11: mounting a group tire from the group of tires on the tire uniformity machine at a random angular position with respect to the rim reference mark;
step 12: collecting tire uniformity data to record a group tire measurement of uniformity data set; and
step 13: subtracting the average machine contribution data set from the group tire measurement of uniformity data set, thereby determining a corrected group tire uniformity data set for the group tire which is free of machine contribution.
According to the invention, the method comprising steps 1 through 13 is further characterized wherein the step 5 includes determining a required quantity of additional measurements of uniformity for the test tire by quantifying and using knowledge of a random variability of tire uniformity measurements through statistical analysis of multiple repeated measurements of tire uniformity on the tire uniformity machine. Alternatively, the step 5 includes determining a required quantity of additional measurements of uniformity for the test tire by specifying the required quantity as a fixed quantity in the range of 20 to 50.
Also according to the invention, the method comprising steps 1 through 13 is further characterized by storing and interpreting the measurement of uniformity data, performing calculations, and processing corrective actions in digitized forms in an arithmetic operation circuit.
According to the invention, the step 6 is further characterized by determining each angular shift from a rotational angle of a peak position of each cross-correlation function.
According to the invention, the method comprising steps 1 through 13 is further characterized by storing the average machine contribution data set that was determined for the test tire; and determining corrected group tire uniformity data sets for additional group tires by repeating for each additional group tire a series of steps comprising the step 11, the step 12, and the step 13. Preferably, the group tire is one in a group of production tires, and the test tire is selected from the group of production tires. Also preferably, the method is further characterized by the step of periodically re-determining the average machine contribution data by selecting the test tire from a current group of production tires; and by repeating a group of steps comprising the step 1 through the step 10.
According to the invention, the method comprising steps 1 through 13 is further characterized by selecting the test tire such that it has the same tire construction as the group of tires to be measured on the tire uniformity machine.
An alternative embodiment of the invention comprises a method for accurately determining a machine contribution of error in tire uniformity measurements made on a tire uniformity machine which subjects a tire to normal conditions of mounting, inflation, load and rotational speed while measuring and collecting tire uniformity measurement data with respect to a rim reference mark, the method characterized by the steps of:
step 1: mounting a tire on the tire uniformity machine at a random angular position with respect to the rim reference mark;
step 2: collecting tire uniformity data to record a first measurement of uniformity data set;
step 3: re-mounting the same tire on the tire uniformity machine at a random angular position with respect to the rim reference mark;
step 4: collecting tire uniformity data to record a repeated measurement of uniformity data set;
step 5: determining if additional measurements of uniformity are required for the tire, then looping back to repeat steps 3 through 5 if additional measurements of uniformity are determined to be required, but proceeding to step 6 when it is determined that additional measurements of uniformity are not required;
step 6: calculating cross-correlation functions and using them to determine angular shifts between the first measurement data set and each of the repeated measurement data sets;
step 7: using the angular shifts to synchronize each repeated measurement data set with the first measurement data set to yield synchronized measurement of uniformity data sets;
step 8: averaging together the first measurement of uniformity data and all of the synchronized measurement of uniformity data sets to yield an average tire uniformity data set that has minimized both random measurement noise and machine contribution errors in the measurement of uniformity data for the tire;
step 9: using the angular shifts to synchronize the average tire uniformity data set with each of the repeated measurement of uniformity data sets, and then subtracting to determine the machine contribution in each tire measurement of uniformity data set to yield machine contribution data sets; and
step 10: averaging together all of the machine contribution data sets to yield an average machine contribution data set for the tire, wherein tire uniformity data has been subtracted out, and random measurement noise has been averaged out to yield a data set that accurately represents the machine contribution of error in tire uniformity measurements performed on the tire uniformity machine.
According to the invention, the steps in the alternative embodiment method are performed using a test tire for the tire, the test tire being selected to be representative of a group of tires to be measured on the tire uniformity machine; preferably selecting the test tire such that it has the same tire construction as the group of tires to be measured on the tire uniformity machine.
According to the alternative embodiment of the invention the step 5 is further characterized by determining a required quantity of additional measurements of uniformity for the tire by quantifying and using knowledge of a random variability of tire uniformity measurements through statistical analysis of multiple repeated measurements of tire uniformity on the tire uniformity machine. Alternatively, a required quantity of additional measurements of uniformity for the tire is determined by specifying the required quantity as a fixed quantity in the range of 20 to 50.
According to the alternative embodiment of the invention, the method is further characterized by storing and interpreting the measurement of uniformity data, performing calculations, and processing corrective actions in digitized forms in an arithmetic operation circuit.
Other aspects, features and advantages of the invention will become apparent in light of the following description thereof.